Rising atmospheric carbon dioxide: plants FACE the future

Uncovering hidden genetic variation in photosynthesis of field-grown maize under ozone pollution

Ozone is the most damaging air pollutant to crops, currently reducing Midwest US maize production by up to 10%, yet there has been very little effort to adapt germplasm for ozone tolerance. Ozone enters plants through stomata, reacts to form reactive oxygen species in the apoplast and ultimately decreases photosynthetic C gain. In this study, 10 diverse inbred parents were crossed in a half-diallel design to create 45 F1 hybrids, which were tested for ozone response in the field using free air concentration enrichment (FACE). Ozone stress increased the heritability of photosynthetic traits and altered genetic correlations among traits. Hybrids from parents Hp301 and NC338 showed greater sensitivity to ozone stress, and disrupted relationships among photosynthetic traits. The physiological responses underlying sensitivity to ozone differed in hybrids from the two parents, suggesting multiple mechanisms of response to oxidative stress. FACE technology was essential to this evaluation because genetic variation in photosynthesis under elevated ozone was not predictable based on performance at ambient ozone. These findings suggest that selection under elevated ozone is needed to identify deleterious alleles in the world's largest commodity crop.

Warming and elevated CO2 alter the transcriptomic response of maize (Zea mays L.) at the silking stage

Exploring the transcriptome of crops in response to warming and elevated CO₂ (eCO₂) is important to gaining insights of botanical adaption and feedback to climate change. This study deployed Illumina sequencing technology to characterize transcriptomic profile of maize plants at the silking stage, which were grown under warming (2 °C higher than ambient temperature) and eCO₂ (550 ppm) conditions. The treatment of ambient temperature and ambient CO₂ concentration was considered as control (CK). Warming, eCO₂ and warming plus eCO₂ resulted in 2732, 1966 and 271 genes expressing differently (DEGs) compared to the CK, respectively. Among the DEGs, 48, 47 and 36 gene ontology (GO) terms were enriched in response to warming, eCO₂ and warming plus eCO₂ compared to the CK, respectively. The majority of genes were assigned to the biological process category and the cellular component category. Elevated CO₂ significantly inhibited gene expressions in terms of photosynthesis and carbohydrate biosynthesis pathways. Warming not only negatively affected expressions of these genes, but also secondary pathways of nitrogen (N) metabolism, including key enzymes of GST30, GST7, GST26, GST15, GLUL and glnA. These results indicated the negative biochemical regulation and physiological functions in maize in response to warming and eCO₂, highlighting the necessity to improve the genetic adaptability of plant to future climate change.

Biotechnological strategies for improved photosynthesis in a future of elevated atmospheric CO2

The improvement of photosynthesis using biotechnological approaches has been the focus of much research. It is now vital that these strategies be assessed under future atmospheric conditions. The demand for crop products is expanding at an alarming rate due to population growth, enhanced affluence, increased per capita calorie consumption, and an escalating need for plant-based bioproducts. While solving this issue will undoubtedly involve a multifaceted approach, improving crop productivity will almost certainly provide one piece of the puzzle. The improvement of photosynthetic efficiency has been a long-standing goal of plant biotechnologists as possibly one of the last remaining means of achieving higher yielding crops. However, the vast majority of these studies have not taken into consideration possible outcomes when these plants are grown long-term under the elevated CO₂ concentrations (e[CO₂]) that will be evident in the not too distant future. Due to the considerable effect that CO₂ levels have on the photosynthetic process, these assessments should become commonplace as a means of ensuring that research in this field focuses on the most effective approaches for our future climate scenarios. In this review, we discuss the main biotechnological research strategies that are currently underway with the aim of improving photosynthetic efficiency and biomass production/yields in the context of a future of e[CO₂], as well as alternative approaches that may provide further photosynthetic benefits under these conditions.

Crop Vulnerability to Weather and Climate Risk: Analysis of Interacting Systems and Adaptation Efficacy for Sustainable Crop Production

Climate change is increasing mean and extreme temperatures in the Southwestern United States, leading to a suite of changes affecting agricultural production. These include changes in water, soils, pathogens, weeds, and pests comprising the production environment. The aim of this synthesis is to describe the anticipated leading agricultural pressures and adaptive responses, many of which are near-term actions with longer-term consequences. In the semiarid Southwestern United States, climate change is expected to increase water scarcity. Surface water shortage is the leading reason for recent diminished crop yields in the Southwest. Drought and lack of water represent the leading regional weather-related cause of crop loss from 1989 to 2017. Thus, water scarcity has been and will continue to be a critical factor leading to regional crop vulnerability. Soils, pathogens, weeds, and insects are components of the agricultural production environment and are directly influenced by near-term weather and long-term climate conditions. Field crops, vegetable crops, and perennial crops have unique production requirements and diverse management options, many already used in farm management, to cope with production environment changes to build climate resilience. Farmers and ranchers continuously respond to changing conditions on a near-term basis. Long-term planning and novel adaptation measures implemented may now build nimble and responsive systems and communities able to cope with future conditions. While decision-support tools and resources are providing increasingly sophisticated approaches to cope with production in the 21st century, we strive to keep pace with the cascading barrage of inter-connected agricultural challenges.

Is triose phosphate utilization involved in the feedback inhibition of photosynthesis in rice under conditions of sink limitation?

This study aimed to understand the physiological basis of rice photosynthetic response to C source-sink imbalances, focusing on the dynamics of the photosynthetic parameter triose phosphate utilization (TPU). Here, rice (Oriza sativa L.) indica cultivar IR64 were grown in controlled environment chambers under current ambient CO2 concentration until heading, and thereafter two CO2 treatments (400 and 800 μmol mol-1) were compared in the presence and absence of a panicle-pruning treatment modifying the C sink. At 2 weeks after heading, photosynthetic parameters derived from CO2 response curves, and non-structural carbohydrate content of flag leaf and internodes were measured three to four times of day. Spikelet number per panicle and flag leaf area on the main culm were recorded. Net C assimilation and TPU decreased progressively after midday in panicle-pruned plants, especially under 800 μmol mol-1 CO2. This TPU reduction was explained by sucrose accumulation in the flag leaf resulting from the sink limitation. Taking together, our findings suggest that TPU is involved in the regulation of photosynthesis in rice under elevated CO2 conditions, and that sink limitation effects should be considered in crop models.

Heritable Changes in Physiological Gas Exchange Traits in Response to Long-Term, Moderate Free-Air Carbon Dioxide Enrichment

Atmospheric carbon dioxide ([CO₂]) concentrations significantly alter developmental plant traits with potentially far-reaching consequences for ecosystem function and productivity. However, contemporary evolutionary responses among extant plant species that coincide with modern, anthropogenically driven [CO₂] rise have rarely been demonstrated among field-grown plant populations. Here we present findings from a long-term, free-air carbon dioxide enrichment (FACE) study in a seminatural European grassland ecosystem in which we observe a differential capacity among plant species to acclimate intrinsic water-use efficiencies (WUEs) in response to prolonged multigenerational exposure to elevated [CO₂] concentrations. In a reciprocal swap trial, using controlled environment growth chambers, we germinated seeds from six of the most dominant plant species at the FACE site [Arrhenatherum elatius (L.), Trisetum flavescens (L.), Holcus lanatus (L.), Geranium pratense (L.), Sanguisorba officinalis (L.), and Plantago lanceolata (L.)]. We found that long-term exposure to elevated [CO₂] strongly influenced the dynamic control of WUE_i in the first filial generations (F₁) of all species as well as an unequal ability to adapt to changes in the [CO₂] of the growth environment among those species. Furthermore, despite trait-environment relationships of this nature often being considered evidence for local adaptation in plants, we demonstrate that the ability to increase WUE_i does not necessarily translate to an ecological advantage in diverse species mixtures.

Carbon assimilation in crops at high temperatures

Global temperatures are rising, and higher rates of temperature increase are projected over land areas that encompass the globe's major agricultural regions. In addition to increased growing season temperatures, heat waves are predicted to become more common and severe. High temperatures can inhibit photosynthetic carbon gain of crop plants and thus threaten productivity, the effects of which may interact with other aspects of climate change. Here, we review the current literature assessing temperature effects on photosynthesis in key crops with special attention to field studies using crop canopy heating technology and in combination with other climate variables. We also discuss the biochemical reactions related to carbon fixation that may limit crop photosynthesis under warming temperatures and the current strategies for adaptation. Important progress has been made on several adaptation strategies demonstrating proof-of-concept for translating improved photosynthesis into higher yields. These are now poised to test in important food crops.

Strong photosynthetic acclimation and enhanced water-use efficiency in grassland functional groups persist over 21 years of CO2 enrichment, independent of nitrogen supply

Uncertainty about long-term leaf-level responses to atmospheric CO₂ rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO₂ (eCO₂ ) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long-lived perennials. Here, we report the effects of eCO₂ on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free-Air CO₂ Enrichment experiment, BioCON. Monocultures of species belonging to C₃ grasses, C₄ grasses, forbs, and legumes were exposed to two levels of CO₂ and nitrogen supply in factorial combinations over 21 years. eCO₂ increased photosynthesis by 12.9% on average in C₃ species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO₂ was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO₂ was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C₄ grasses the least as expected, but did not further diverge over time. Leaf-level water-use efficiency increased by 50% under eCO₂ primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO₂ in nitrogen-limited systems, and that significant and consistent declines in stomatal conductance and increases in water-use efficiency under eCO₂ may allow plants to better withstand drought.

The effect of pre-industrial and predicted atmospheric CO2 concentrations on the development of diazotrophic and non-diazotrophic cyanobacterium: Dolichospermum circinale and Microcystis aeruginosa

Photoautotrophs are capable of consuming high quantities of CO₂, yet scant research exists examining the influence of different CO₂ concentrations on the growth of freshwater diazotrophic or non-diazotrophic cyanobacteria. In this study, we cultured two cyanobacteria taxa (Dolichospermum circinale and Microcystis aeruginosa) within controlled atmospheric CO₂ chambers at pre-industrial, and post-industrial concentrations. Biovolume and chlorophyll a (Chl-a) differed as a consequence of the adjusted CO₂ gradients. Significantly higher biovolume measurements were observed in the elevated CO₂ treatment for the diazotrophic species in the initial experiment. However, a follow-up experiment, with a corrected culture replenishment regime showed Chl-a measurements were greater for the diazotrophic and non-diazotrophic species in the elevated CO₂ treatment. Increasing CO₂ presents a risk to already compromised eutrophic and hyper-eutrophic ecosystems, and we reason increasing CO₂ concentrations could affect photosynthetic performance and CO₂ assimilation of surface dwelling cyanobacteria. Further experimental work is required to establish ecological thresholds for freshwater ecosystems, as pH levels showed a measurable reduction within the elevated CO₂ treatments. As cyanobacteria species may respond quite differently to future CO₂ concentrations similar comparative studies should be carried out that focus on CO₂ dynamics and pH. The findings of the study indicate diazotrophic cyanobacteria growth in particular may benefit from elevated atmospheric CO₂ concentrations.

Divergent long-term trends and interannual variation in ecosystem resource use efficiencies of a southern boreal old black spruce forest 1999-2017

Long-term trends in ecosystem resource use efficiencies (RUEs) and their controlling factors are key pieces of information for understanding how an ecosystem responds to climate change. We used continuous eddy covariance and microclimate data over the period 1999-2017 from a 120-year-old black spruce stand in central Saskatchewan, Canada, to assess interannual variability, long-term trends, and key controlling factors of gross ecosystem production (GEP) and the RUEs of carbon (CUE = net primary production [NPP]/GEP), light (LUE = GEP/absorbed photosynthetic radiation [APAR]), and water (WUE = GEP/evapotranspiration [E]). At this site, annual GEP has shown an increasing trend over the 19 years (p < 0.01), which may be attributed to rising atmospheric CO₂ concentration. Interannual variability in GEP, aside from its increasing trend, was most strongly related to spring temperatures. Associated with the significant increase in annual GEP were relatively small changes in NPP, APAR, and E, so that annual CUE showed a decreasing trend and annual LUE and WUE showed increasing trends over the 19 years. The long-term trends in the RUEs were related to the increasing CO₂ concentration. Further analysis of detrended RUEs showed that their interannual variation was impacted most strongly by air temperature. Two-factor linear models combining CO₂ concentration and air temperature performed well (R² ~0.60) in simulating annual RUEs. LUE and WUE were positively correlated both annually and seasonally, while LUE and CUE were mostly negatively correlated. Our results showed divergent long-term trends among CUE, LUE, and WUE and highlighted the need to account for the combined effects of climatic controls and the 'CO₂ fertilization effect' on long-term variations in RUEs. Since most RUE-based models rely primarily on one resource limitation, the observed patterns of relative change among the three RUEs may have important implications for RUE-based modeling of C fluxes.

Perspective: Understanding the Intersection of Climate/Environmental Change, Health, Agriculture, and Improved Nutrition - A Case Study: Type 2 Diabetes

Efforts to promote health through improved diet and nutrition demand an appreciation of the nutritional ecology that accounts for the intersection of agriculture, food systems, health, disease and a changing environment. The complexity and implications of this ecology is exemplified by current trends and efforts to address nutrition-related non-communicable diseases (NCDs), most prominently type 2 diabetes. The global prevalence of type 2 diabetes continues to rise unabated. Of particular concern is how to address the unhealthy dietary patterns that are contributing to this pandemic in a changing environment. A multi- disciplinary approach is required that will engage those communities that comprise the continuum of effort from research to translation and implementation of evidence-informed interventions, programs and policies. Using the prevention of type 2 diabetes by increasing fruit and vegetable consumption as an exemplar, we argue that the ability to effect positive change in this and other persistent nutrition-related problems can be achieved by moving away from siloed approaches that limit the integration of key components of the diet-health continuum. Ultimately the impact of preventing type 2 diabetes via increased fruit and vegetable consumption will depend on how the entire diet changes, not just fruits and vegetables. In addition, the rapidly changing physical environment that will confront our food production system going forward will also shape the interventions that are possible. Nonetheless, the proposed "team science" approach that accounts for all the elements of the nutrition ecology will better position us to achieve public health goals through safe and sustainable food systems.

Growth and photosynthetic responses in Brassica napus differ during stress and recovery periods when exposed to combined heat, drought and elevated CO2

This study was intended to investigate how an agronomically important crop Brassica napus will be able to cope with the combined impact of a heatwave (21/14 °C vs. 33/26 °C day/night) and drought under ambient or elevated CO₂ (800 vs. 400 μmol mol^-1) and to what degree their recovery will be ensured after the stress, when additional CO₂ is also removed. The obtained results revealed that, in the presence of an adequate water supply, B. napus performed well under heatwave conditions. However, drought fully negated all the advantages gained from hotter climate and led to a slower and incomplete recovery of gas exchange and retarded growth after the stress, regardless mitigating the effect of elevated CO₂ during the stress. The mechanism by which the elevated CO₂ diminished the adverse effect of a combined heat and drought stress on photosynthetic rate at saturating light (A_sat) was attributed to the improved plant water relations. However, it had little effect on the recovery of A_sat. In contrast, the mechanism by which photosynthesis was more impaired under the combination of heatwave and drought, compared to single drought treatment, was attributed mainly to the faster soil drying as well as faster and sharper decrease in stomatal conductance and subsequent in C_i/C_a. Keeping in mind that photosynthesis can acclimatize by downregulation to higher CO₂, the results of this study, showing a weak memory of mitigating the effect of elevated CO₂, highlight a potential risk of more intense and frequent heatwaves and droughts on B. napus.

Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency

Forests remove about 30% of anthropogenic CO₂ emissions through photosynthesis and return almost 40% of incident precipitation back to the atmosphere via transpiration. The trade-off between photosynthesis and transpiration through stomata, the water-use efficiency (WUE), is an important driver of plant evolution and ecosystem functioning, and has profound effects on climate. Using stable carbon and oxygen isotope ratios in tree rings, we found that WUE has increased by a magnitude consistent with estimates from atmospheric measurements and model predictions. Enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to moisture-limited forests. This result points to smaller reductions in transpiration in response to increasing atmospheric CO₂, with important implications for forest–climate interactions, which remain to be explored.

Multiple lines of evidence suggest that plant water-use efficiency (WUE)—the ratio of carbon assimilation to water loss—has increased in recent decades. Although rising atmospheric CO₂ has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO₂-induced reductions in stomatal conductance.

Assessing interactions between environmental factors and aquatic toxicity: Influences of dissolved CO2 and light on Cd toxicity in the aquatic macrophyte Potamogeton crispus

The objective of this study was to investigate the combined effects of varying dissolved CO₂ concentration (ambient CO₂, 3˜17 μmol L^-1, elevated CO₂, 48˜81 μmol L^-1) and light intensity (high light, c. 150 μmol photon m^-2 s^-1, low light, c. 25 μmol photon m^-2 s^-1) on the bioaccumulation and phytotoxicity of cadmium (Cd) in a macrophyte Potamogeton crispus, under constant Cd exposure. The data confirmed that 100 μM Cd led to adverse changes in morphology, ultrastructure and biochemistry in P. crispus. The toxic effects depended strongly on CO₂ concentration and light intensity: elevated CO₂ and high light both increased Cd concentrations in P. crispus, and there was a significant interaction between the two factors. Compared to high light grown plants, the photochemical efficiency and chlorophyll content of low light grown P. crispus were much less affected and the MDA content was lower, when exposed to 100 μM Cd. In addition, an antioxidative response was observed with a significant increase in SOD, POD and GST activities, indicating that low light grown P. crispus are more protected against Cd toxicity. When compared with ambient CO₂ concentrations, chlorophyll content, chlorophyll fluorescence, photosynthetic rate and starch content, as well as the activity of SOD and GST, were significantly enhanced in Cd treated P. crispus under elevated CO₂. This suggests that elevated CO₂ reduced Cd toxicity in P. crispus by increasing photosynthesis and enhancing the antioxidant system. Moreover, the statistical results showed that dissolved CO₂ and light had additive effects on Cd toxicity in P. crispus, reflected by the physiological parameters of total chlorophyll content, SOD activity and MDA content, indicating that the combination of high CO₂ and low light produced more protection against Cd toxicity than did the factors alone. Based on the results of this study, it appears clear that referring to a specific site in aquatic ecosystem, dissolved CO₂ concentration and light availability should be considered when assessing and managing Cd impacts on aquatic plants.

Direct evidence for modulation of photosynthesis by an arbuscular mycorrhiza-induced carbon sink strength

It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and downregulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence. We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected the photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily. Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10-40%) decline in photosynthetic rates that lasted from 30 min to several hours in plants that were well-nourished and hydrated, and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700 ppm) atmospheric CO₂ . This is the first direct experimental evidence for the C sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source-sink relations, and may have strong implications in large-scale assessments and modelling of plant photosynthesis.

Elevated CO2 concentration induces photosynthetic down-regulation with changes in leaf structure, non-structural carbohydrates and nitrogen content of soybean

BACKGROUND

Understanding the mechanisms of crops in response to elevated CO2 concentrations is pivotal to estimating the impacts of climate change on the global agricultural production. Based on earlier results of the "doubling-CO2 concentration" experiments, many current climate models may overestimate the CO2 fertilization effect on crops, and meanwhile, underestimate the potential impacts of future climate change on global agriculture ecosystem when the atmospheric CO2 concentration goes beyond the optimal levels for crop growth.

RESULTS

This study examined the photosynthetic response of soybean (Glycine max (L.) Merr.) to elevated CO2 concentration associated with changes in leaf structure, non-structural carbohydrates and nitrogen content with environmental growth chambers where the CO2 concentration was controlled at 400, 600, 800, 1000, 1200, 1400, 1600 ppm. We found CO2-induced down-regulation of leaf photosynthesis as evidenced by the consistently declined leaf net photosynthetic rate (An) with elevated CO2 concentrations. This down-regulation of leaf photosynthesis was evident in biochemical and photochemical processes since the maximum carboxylation rate (Vcmax) and the maximum electron transport rate (Jmax) were dramatically decreased at higher CO2 concentrations exceeding their optimal values of about 600 ppm and 400 ppm, respectively. Moreover, the down-regulation of leaf photosynthesis at high CO2 concentration was partially attributed to the reduced stomatal conductance (Gs) as demonstrated by the declines in stomatal density and stomatal area as well as the changes in the spatial distribution pattern of stomata. In addition, the smaller total mesophyll size (palisade and spongy tissues) and the lower nitrogen availability may also contribute to the down-regulation of leaf photosynthesis when soybean subjected to high CO2 concentration environment.

CONCLUSIONS

Down-regulation of leaf photosynthesis associated with the changes in stomatal traits, mesophyll tissue size, non-structural carbohydrates, and nitrogen availability of soybean in response to future high atmospheric CO2 concentration and climate change.

Differential Regulation of Stomatal Conductance as a Strategy to Cope With Ammonium Fertilizer Under Ambient Versus Elevated CO2

While nitrogen (N) derived from ammonium would be energetically less expensive than nitrate-derived N, the use of ammonium-based fertilizer is limited by the potential for toxicity symptoms. Nevertheless, previous studies have shown that exposure to elevated CO2 favors ammonium assimilation in plants. However, little is known about the impact of different forms of N fertilizer on stomatal opening and their consequent effects on CO2 and H2O diffusion in wheat plants exposed to ambient and elevated CO2. In this article, we have examined the response of the photosynthetic machinery of durum wheat (Triticum durum, var. Amilcar) grown with different types of N fertilizer (NO3 -, NH4 +, and NH4NO3) at 400 versus 700 ppm of CO2. Alongside gas exchange and photochemical parameters, the expression of genes involved in CO2 (PIP1.1 and PIP2.3) and H2O (TIP1) diffusion as well as key C and N primary metabolism enzymes and metabolites were studied. Our results show that at 400 ppm CO2, wheat plants fertilized with ammonium as the N source had stress symptoms and a strong reduction in stomatal conductance, which negatively affected photosynthetic rates. The higher levels of PIP1.1 and PIP2.3 expression in ammonium-fertilized plants at 400 ppm CO2 might reflect the need to overcome limitations to the CO2 supply to chloroplasts due to restrictions in stomatal conductance. This stomatal limitation might be associated with a strategy to reduce ammonium transport toward leaves. On the other hand, ammonium-fertilized plants at elevated CO2 did not show stress symptoms, and no differences were detected in stomatal opening or water use efficiency (WUE). Moreover, similar gene expression of the aquaporins TIP1, PIP1.1, and PIP2.3 in ammonium-fertilized plants grown at 700 ppm compared to nitrate and ammonium nitrate plants would suggest that an adjustment in CO2 and H2O diffusion is not required. Therefore, in the absence of a stress context triggered by elevated CO2, ammonium- and ammonium nitrate-fertilized plants were able to increase their photosynthetic rates, which were translated eventually into higher leaf protein content.

Elevated CO2 Increases Root Mass and Leaf Nitrogen Resorption in Red Maple (Acer rubrum L.)

To understand whether the process of seasonal nitrogen resorption and biomass allocation are different in CO2-enriched plants, seedlings of red maple (Acer rubrum L.) were exposed to three CO2 concentrations (800 µL L−1 CO2 treatments—A800, 600 µL L−1 CO2 treatments—A600, and 400 µL L−1 CO2 treatments—A400) in nine continuous stirred tank reactor (CSTR) chambers. Leaf mass per area, leaf area, chlorophyll index, carbon (C), nitrogen (N) contents, nitrogen resorption efficiency (NRE), and biomass allocation response were investigated. The results indicated that: (1) Significant leaf N decline was found in senescent leaves of two CO2 treatments, which led to an increase of 43.4% and 39.7% of the C/N ratio in A800 and A600, respectively. (2) Elevated CO2 induced higher NRE, with A800 and A600 showing significant increments of 50.3% and 46.2%, respectively. (3) Root biomass increased 33.1% in A800 and thus the ratio of root to shoot ratio was increased by 25.8%. In conclusion, these results showed that to support greater nutrient and water uptake and the continued response of biomass under elevated CO2, Acer rubrum partitioned more biomass to root and increased leaf N resorption efficiency.

Improving Potato Stress Tolerance and Tuber Yield Under a Climate Change Scenario - A Current Overview

Global climate change in the form of extreme heat and drought poses a major challenge to sustainable crop production by negatively affecting plant performance and crop yield. Such negative impact on crop yield is likely to be aggravated in future because continued greenhouse gas emissions will cause further rise in temperature leading to increased evapo-transpiration and drought severity, soil salinity as well as insect and disease threats. This has raised a major challenge for plant scientists on securing global food demand, which urges an immediate need to enhance the current yield of major food crops by two-fold to feed the increasing population. As a fourth major food crop, enhancing potato productivity is important for food security of an increasing population. However, potato plant is highly prone to high temperature, drought, soil salinity, as well as insect and diseases. In order to maintain a sustainable potato production, we must adapt our cultivation practices and develop stress tolerant potato cultivars that are appropriately engineered for changing environment. Yet the lack of data on the underlying mechanisms of potato plant resistance to abiotic and biotic stress and the ability to predict future outcomes constitutes a major knowledge gap. It is a challenge for plant scientists to pinpoint means of improving tuber yield under increasing CO2, high temperature and drought stress including the changing patterns of pest and pathogen infestations. Understanding stress-related physiological, biochemical and molecular processes is crucial to develop screening procedures for selecting crop cultivars that can better adapt to changing growth conditions. Elucidation of such mechanism may offer new insights into the identification of specific characteristics that may be useful in breeding new cultivars aimed at maintaining or even enhancing potato yield under changing climate. This paper discusses the recent progress on the mechanism by which potato plants initially sense the changes in their surrounding CO2, temperature, water status, soil salinity and consequently respond to these changes at the molecular, biochemical and physiological levels. We suggest that future research needs to be concentrated on the identification and characterization of signaling molecules and target genes regulating stress tolerance and crop yield potential.

Effects of Elevated CO2 on Wheat Yield: Non-Linear Response and Relation to Site Productivity

Elevated carbon dioxide (eCO2) is well known to stimulate plant photosynthesis and growth. Elevated carbon dioxide’s effects on crop yields are of particular interest due to concerns for future food security. We compiled experimental data where field-grown wheat (Triticum aestivum Linnaeus) was exposed to different CO2 concentrations. Yield and yield components were analyzed by meta-analysis to estimate average effects, and response functions derived to assess effect size in relation to CO2 concentration. Grain yield increased by 26% under eCO2 (average ambient concentration of 372 ppm and elevated 605 ppm), mainly due to the increase in grain number. The response function for grain yield with CO2 concentration strongly suggests a non-linear response, where yield stimulation levels off at ~600 ppm. This was supported by the meta-analysis, which did not indicate any significant difference in yield stimulation in wheat grown at 456–600 ppm compared to 601–750 ppm. Yield response to eCO2 was independent of fumigation technique and rooting environment, but clearly related to site productivity, where relative CO2 yield stimulation was stronger in low productive systems. The non-linear yield response, saturating at a relatively modest elevation of CO2, was of large importance for crop modelling and assessments of future food production under rising CO2.

Suppressing photorespiration for the improvement in photosynthesis and crop yields: A review on the role of S-allantoin as a nitrogen source

Environmental variations resulting in biotic and abiotic stresses demand adaptive changes in the photosynthetic machinery. To cope with these challenges, plant scientists are constantly striving to enhance photosynthetic activity. The photorespiration pathway, which fixes O₂ and releases CO₂ in C₃ plants, competes with photosynthesis. One method to increase yield would be to enhance photosynthesis by engineering the photorespiratory pathway. To date, three engineered photorespiratory pathways have been produced, of which two have been proven experimentally in the model plant, Arabidopsis thaliana. These approaches might be helpful in enhancing crop resilience to future environmental challenges. In partially photorespiratory suppressed plants, it is hypothesized that a gene cluster may have formed between bacterial glycolate dehydrogenase (GDH), glyoxylate carboligase (GCL), and tartronic semi aldehyde (TSR) genes with Arabidopsis allantoin degradation genes like Arabidopsis allantoinase (AtALN) to utilize S-allantoin as a source of nitrogen. Observations of the use of allantoin as an exclusive source of nitrogen or energy by Arabidopsis and Escherichia coli led us to propose a genetic switch control model between nitrogen assimilation and energy producing pathways in partially photorespiratory suppressed plants.

Projections of water, carbon, and nitrogen dynamics under future climate change in an old-growth Douglas-fir forest in the western Cascade Range using a biogeochemical model

Statistically downscaled climate change scenarios from four General Circulation Models for two Representative Concentration Pathways (RCP) were applied as inputs to a biogeochemical model, PnET-BGC, to examine potential future dynamics of water, carbon, and nitrogen in an old-growth Douglas-fir forest in the western Cascade Range. Projections show 56% to 77% increases in stomatal conductance throughout the year from 1986-2010 to 2076-2100, and 65% to 104% increases in leaf carbon assimilation between October and June over the same period. However, future dynamics of water and carbon under the RCP scenarios are affected by a 49% to 86% reduction in foliar biomass resulting from severe air temperature and humidity stress to the forest in summer. Important implications of future decreases in foliar biomass include 1) 20% to 71% decreases in annual transpiration which increase soil moisture by 7% to 15% in summer and fall; 2) decreases in photosynthesis by 77% and soil organic matter by 62% under the high radiative forcing scenario; and 3) altered foliar and soil carbon to nitrogen stoichiometry. Potential carbon dioxide fertilization effects on vegetation are projected to 1) amplify decreases in transpiration by 4% to 9% and increases in soil moisture in summer and fall by 1% to 2%; and 2) alleviate decreases in photosynthesis by 4%; while 3) having negligible effects on the dynamics of nitrogen. Our projections suggest that future decrease in transpiration and moderate water holding capacity may mitigate soil moisture stress to the old-growth Douglas-fir forest. Future increases in nitrogen concentration in soil organic matter are projected to alleviate the decrease in net nitrogen mineralization despite a reduction in decomposition of soil organic matter by the end of the century.

Interspecific differences in how sink-source imbalance causes photosynthetic downregulation among three legume species

BACKGROUND AND AIMS

Sink-source imbalance could cause an accumulation of total non-structural carbohydrates (TNC; soluble sugar and starch) in source leaves. We aimed to clarify interspecific differences in how sink-source imbalance and TNC causes the downregulation of photosynthesis among three legume plants. The TNC in source leaves was altered by short-term manipulative treatments, and its effects on photosynthetic characteristics were evaluated.

METHODS

Soybean, French bean and azuki bean were grown under high nitrogen availability. After primary leaves were fully expanded, they were subjected to additional treatments: defoliation except for two primary leaves; transfer to low nitrogen conditions; transfer to low nitrogen conditions and defoliation; or irradiation by light-emitting diodes. Physiological and anatomical traits such as TNC content, maximum photosynthetic rate, cell wall content and δ13C values of primary leaves and whole-plant growth were examined.

KEY RESULTS

Among the three legume plants, the downregulation of maximum photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content was co-ordinated with an increase in TNC only in French bean. Rubisco did not decrease with an increase in TNC in soybean and azuki bean. The defoliation treatment caused an increase in cell wall content especially in soybean, and maximum photosynthesis decreased despite resulting in a higher Rubisco content. This indicates that a decrease in mesophyll conductance could cause photosynthetic downregulation, which was confirmed by an increase in δ13C.

CONCLUSION

The present results suggest that a downregulation of photosynthesis in response to increased levels of TNC in source leaves can result not only from decreases in Rubisco content, but also from anatomical factors, such as an increase in cell wall thickness leading to reduced chloroplast CO2 concentrations.

Effects of elevated CO2 concentration on leaves and berries of black elder (Sambucus nigra) using UHPLC-ESI-QTOF-MS/MS and gas exchange measurements

The effect of elevated CO₂ concentration on leaves of black elder (Sambucus nigra) was investigated based on leaf gas exchange, chlorophyll content as well as on the analysis of the underlying metabolite profile of the fruits. The measurements were carried out once a month over a period of time of 4 months. The CO₂ uptake rate, the transpiration rate and stomatal conductance were significantly higher in plants under ambient CO₂, in comparison to plants grown under elevated CO₂ concentrations. On the other hand, at the initial phase of the experiments, the photosynthesis rate was higher in CO₂ loaded plants compared to plants grown under normal conditions. Remarkably, after about one month a habituation effect could be observed leading to a decrease of the photosynthetic efficiency approaching again the normal level. To understand the observed effects on a molecular level, non-targeted fingerprinting analysis was performed on the ripe elder berries using LC-qToF-ESI-MS(/MS). Differences in the composition of various phenols, triglycerides and PC (36:5) as well as a stigmasterole-derivate could be detected. In contrast, central metabolic pathways such as photosynthesis, the tricarboxylic acid cycle as well as the biosynthesis of essential amino acids obviously are not considerably affected.

Short-term responses of soybean roots to individual and combinatorial effects of elevated [CO2] and water deficit

Climate change increasingly threatens plant growth and productivity. Soybean (Glycine max) is one of the most important crops in the world. Although its responses to increased atmospheric carbon dioxide concentration ([CO2]) have been previously studied, root molecular responses to elevated [CO2] (E[CO2]) or the combination/interaction of E[CO2] and water deficit remain unexamined. In this study, we evaluated the individual and combinatory effects of E[CO2] and water deficit on the physiology and root molecular responses in soybean. Plants growing under E[CO2] exhibited increased photosynthesis that resulted in a higher biomass, plant height, and leaf area. E[CO2] decreased the transcripts levels of genes involved in iron uptake and transport, antioxidant activity, secondary metabolism and defense, and stress responses in roots. When plants grown under E[CO2] are treated with instantaneous water deficit, E[CO2] reverted the expression of water deficit-induced genes related to stress, defense, transport and nutrient deficiency. Furthermore, the interaction of both treatments uniquely affected the expression of genes. Both physiological and transcriptomic analyses demonstrated that E[CO2] may mitigate the negative effects of water deficit on the soybean roots. In addition, the identification of genes that are modulated by the interaction of E[CO2] and water deficit suggests an emergent response that is triggered only under this specific condition.

Increased temperatures may safeguard the nutritional quality of crops under future elevated CO2 concentrations

Iron (Fe) and zinc (Zn) deficiencies are a global human health problem that may worsen by the growth of crops at elevated atmospheric CO2 concentration (eCO2 ). However, climate change will also involve higher temperature, but it is unclear how the combined effect of eCO2 and higher temperature will affect the nutritional quality of food crops. To begin to address this question, we grew soybean (Glycine max) in a Temperature by Free-Air CO2 Enrichment (T-FACE) experiment in 2014 and 2015 under ambient (400 μmol mol-1 ) and elevated (600 μmol mol-1 ) CO2 concentrations, and under ambient and elevated temperatures (+2.7°C day and +3.4°C at night). In our study, eCO2 significantly decreased Fe concentration in soybean seeds in both seasons (-8.7 and -7.7%) and Zn concentration in one season (-8.9%), while higher temperature (at ambient CO2 concentration) had the opposite effect. The combination of eCO2 with elevated temperature generally restored seed Fe and Zn concentrations to levels obtained under ambient CO2 and temperature conditions, suggesting that the potential threat to human nutrition by increasing CO2 concentration may not be realized. In general, seed Fe concentration was negatively correlated with yield, suggesting inherent limitations to increasing seed Fe. In addition, we confirm our previous report that the concentration of seed storage products and several minerals varies with node position at which the seeds developed. Overall, these results demonstrate the complexity of predicting climate change effects on food and nutritional security when various environmental parameters change in an interactive manner.

Short-term effects of high CO2 accelerate photosynthetic induction in Populus koreana × trichocarpa with always-open stomata regardless of phenotypic changes in high CO2 growth conditions

Long-term high CO2 exposure accelerates photosynthetic induction response due to rapid light increase. However, it is unclear whether the acceleration is caused by acclimation of photosynthetic components (long-term CO2 effect) and/or by the sufficient substrate under high CO2 at the measurement (short-term CO2 effect). Populus koreana × trichocarpa cv. Peace has wide-open stomata almost not responding to changes of photon flux density. Using this species, we examined the long- and short-term CO2 effects on photosynthetic induction by focusing on biochemical components. We grew the plants under [CO2] of 380, 700 and 1020 μmol CO2 mol-1 air and measured the photosynthetic induction response under [CO2] of 380 and 1020 μmol CO2 mol-1 air. Despite significant reduction in Rubisco content and light-saturated photosynthetic rate in the leaves from the high growth CO2, the photosynthetic induction time was similar in leaves from different growth CO2 plants when measurement [CO2] was the same. The induction, however, was significantly fast at the higher than at the lower measurement [CO2], regardless of growth CO2 of the plants. These results demonstrate that the acceleration of apparent photosynthetic induction under high CO2 environment was mainly contributed by a short-term CO2 effect rather than by a long-term acclimation effect when stomatal limitation is not the major factor.

The Integration of Algal Carbon Concentration Mechanism Components into Tobacco Chloroplasts Increases Photosynthetic Efficiency and Biomass

Increasing the productivity of crops is a major challenge in agricultural research. Given that photosynthetic carbon assimilation is necessary for plant growth, enhancing the efficiency of photosynthesis is one strategy to boost agricultural productivity. The authors attempted to increase the photosynthetic efficiency and biomass of tobacco plants by expressing individual components of the Chlamydomonas reinhardtii carbon concentration mechanism (CCM) and integrating them into the chloroplast. Independent transgenic varieties are generated accumulating the carbonic anhydrase CAH3 in the thylakoid lumen or the bicarbonate transporter LCIA in the inner chloroplast membrane. Independent homozygous transgenic lines showed enhanced CO2 uptake rates (up to 15%), increased photosystem II efficiency (by up to 18%), and chlorophyll content (up to 19%). Transgenic lines produced more shoot biomass than wild-type and azygous controls, and accumulated more carbohydrate and amino acids, reflecting the higher rate of photosynthetic CO2 fixation. These data demonstrate that individual algal CCM components can be integrated into C3 plants to increase biomass, suggesting that transgenic lines combining multiple CCM components could further increase the productivity and yield of C3 crops.

Elevated CO2 (free-air CO2 enrichment) increases grain yield of aluminium-resistant but not aluminium-sensitive wheat (Triticum aestivum) grown in an acid soil

BACKGROUND AND AIMS

Soil acidity currently limits root growth and crop production in many regions, and climate change is leading to uncertainties regarding future food supply. However, it is unknown how elevated CO2 (eCO2) affects the performance of wheat crops in acid soils under field conditions. We investigated the effects of eCO2 on plant growth and yield of three pairs of near-isogenic hexaploid wheat lines differing in alleles of aluminium-resistant genes TaALMT1 (conferring root malate efflux) and TaMATE1B (conferring citrate efflux).

METHODS

Plants were grown until maturity in an acid soil under ambient CO2 (aCO2; 400 µmol mol-1) and eCO2 (550 µmol mol-1) in a soil free-air CO2 enrichment facility (SoilFACE). Growth parameters and grain yields were measured.

KEY RESULTS

Elevated CO2 increased grain yield of lines carrying TaMATE1B by 22 % and lines carrying only TaALMT1 by 31 %, but did not increase the grain yield of Al3+-sensitive lines. Although eCO2 promoted tiller formation, coarse root length and root biomass of lines carrying TaMATE1B, it did not affect ear number, and it therefore limited yield potential. By contrast, eCO2 decreased or did not change these parameters for lines carrying only TaALMT1, and enhanced biomass allocation to grains thereby resulting in increased grain yield. Despite TaMATE1B being less effective than TaALMT1 at conferring Al3+ resistance based on root growth, the gene promoted grain yield to a similar level to TaALMT1 when the plants were grown in acid soil. Furthermore, TaALMT1 and TaMATE1B were not additive in their effects.

CONCLUSIONS

As atmospheric CO2 increases, it is critical that both Al3+-resistance genes (particularly TaALMT1) should be maintained in hexaploid wheat germplasm in order for yield increases from CO2 fertilization to be realized in acid soils.

Effects of water deficit stress on agronomic and physiological responses of rice and greenhouse gas emission from rice soil under elevated atmospheric CO2

Rice is the foremost staple food in the world, safeguarding the global food and nutritional security. Rise in atmospheric carbon dioxide (CO₂) and water deficits are threatening global rice productivity and sustainability. Under real field conditions these climatic factors often interact with each other resulting in impacts that are remarkably different compared to individual factor exposure. Rice soils exposed to drought and elevated CO₂ (eCO₂) alters the biomass, diversity and activity of soil microorganisms affecting greenhouse gas (GHG) emission dynamics. In this review we have discussed the impacts of eCO₂ and water deficit on agronomic, biochemical and physiological responses of rice and GHGs emissions from rice soils. Drought usually results in oxidative stress due to stomatal closure, dry weight reduction, formation of reactive oxygen species, decrease in relative water content and increase in electrolyte leakage at almost all growth and developmental phases of rice. Elevated atmospheric CO₂ concentration reduces the negative effects of drought by improving plant water relations, reducing stomatal opening, decreasing transpiration, increasing canopy photosynthesis, shortening crop growth period and increasing the antioxidant metabolite activities in rice. Increased scientific understanding of the effects of drought and eCO₂ on rice agronomy, physiology and GHG emission dynamics of rice soil is essential for devising adaptation options. Integration of novel agronomic practices viz., crop establishment methods and alternate cropping systems with improved water and nutrient management are important steps to help rice farmers cope with drought and eCO₂. The review summarizes future research needs for ensuring sustained global food security under future warmer, drier and high CO₂ conditions.

Atmospheric pCO2 impacts leaf structural and physiological traits in Quercus petraea seedlings

Atmospheric p CO ₂ impacts Quercus petraea biomass production and cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhances foliar non-structural carbohydrate levels and sucrose contents in a pCO ₂ concentration-dependent manner. Sessile oak (Quercus petraea Liebl.) was grown for ca. half a year from seeds at ambient control (525 ppm), 750, 900, and 1000 ppm atmospheric pCO₂ under controlled conditions. Increasing pCO₂ enhanced biomass production, modified the cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhanced the foliar non-structural carbohydrate level, in particular the sucrose content; as well as total N content of leaves by increased levels of all major N fractions, i.e., soluble proteins, total amino acids, and structural N. The enhanced total amino acid level was largely due to 2-ketoglutarate and oxalo acetate-derived compounds. Increasing pCO₂ alleviated oxidative stress in the leaves as indicated by reduced H₂O₂ contents. High in vitro glutathione reductase activity at reduced H₂O₂ contents suggests enhanced ROS scavenging, but increased lipid peroxidation may also have contributed, as indicated by a negative correlation between malone dialdehyde and H₂O₂ contents. Almost all these effects were at least partially reversed, when pCO₂ exceeded 750 or 900 ppm. Apparently, the interaction of atmospheric pCO₂ with leaf structural and physiological traits of Q. petraea seedlings is characterized by a dynamic response depending on the pCO₂ level.

Effects of CO2 application and endophytic bacterial inoculation on morphological properties, photosynthetic characteristics and cadmium uptake of two ecotypes of Sedum alfredii Hance

Plant uptake of cadmium (Cd) is affected by soil and environmental conditions. In this study, hydroponic experiments were conducted to investigate the effects of elevated CO₂ coupled with inoculated endophytic bacteria M002 on morphological properties, gas exchange, photosynthetic pigments, chlorophyll fluorescence, and Cd uptake of S. alfredii. The results showed that bio-fortification processes (elevated CO₂ and/or inoculated with endophytic bacteria) significantly (p < 0.05) promoted growth patterns, improved photosynthetic characteristics and increased Cd tolerance of both ecotypes of S. alfredii, as compared to normal conditions. Net photosynthetic rate (Pn) in intact leaves of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) were increased by 73.93 and 32.90%, respectively at the low Cd (2 μM), 84.41 and 57.65%, respectively at the high Cd level (10 μM). Superposition treatment increased Cd concentration in shoots and roots of HE, by 50.87 and 82.12%, respectively at the low Cd and 46.75 and 88.92%, respectively at the high Cd level. Besides, superposition treatment declined Cd transfer factor of NHE, by 0.85% at non-Cd rate, 17.22% at the low Cd and 22.26% at the high Cd level. These results indicate that elevated CO₂ coupled with endophytic bacterial inoculation may effectively improve phytoremediation efficiency of Cd-contaminated soils by hyperaccumulator, and alleviate Cd toxicity to non-hyperaccumulator ecotype of Sedum alfredii.

Plant carbon metabolism and climate change: elevated CO2 and temperature impacts on photosynthesis, photorespiration and respiration

Contents Summary 32 I. The importance of plant carbon metabolism for climate change 32 II. Rising atmospheric CO2 and carbon metabolism 33 III. Rising temperatures and carbon metabolism 37 IV. Thermal acclimation responses of carbon metabolic processes can be best understood when studied together 38 V. Will elevated CO2 offset warming-induced changes in carbon metabolism? 40 VI. No plant is an island: water and nutrient limitations define plant responses to climate drivers 41 VII. Conclusions 42 Acknowledgements 42 References 42 Appendix A1 48 SUMMARY: Plant carbon metabolism is impacted by rising CO₂ concentrations and temperatures, but also feeds back onto the climate system to help determine the trajectory of future climate change. Here we review how photosynthesis, photorespiration and respiration are affected by increasing atmospheric CO₂ concentrations and climate warming, both separately and in combination. We also compile data from the literature on plants grown at multiple temperatures, focusing on net CO₂ assimilation rates and leaf dark respiration rates measured at the growth temperature (A_growth and R_growth , respectively). Our analyses show that the ratio of A_growth to R_growth is generally homeostatic across a wide range of species and growth temperatures, and that species that have reduced A_growth at higher growth temperatures also tend to have reduced R_growth , while species that show stimulations in A_growth under warming tend to have higher R_growth in the hotter environment. These results highlight the need to study these physiological processes together to better predict how vegetation carbon metabolism will respond to climate change.

Developing Transgenic Agronomic Traits for Crops: Targets, Methods, and Challenges

The last two decades have witnessed a surge of investment by the agricultural biotechnology industry in the development of transgenic agronomic traits. These are traits that improve yield performance by modifying endogenous physiological processes such as energy capture, nutrient utilization, and stress tolerance. In this chapter we provide a foundation for understanding these fundamental processes and then outline approaches that have been taken to use this knowledge for yield improvement. We characterize the current status of product development pipelines in the industry and illustrate the trait discovery process with three important examples-bacterial cold-shock proteins, alanine aminotransferase, and auxin-regulated genes. The challenges with developing and commercializing an agronomic trait product are discussed.

Extreme climatic events down-regulate the grassland biomass response to elevated carbon dioxide

Terrestrial ecosystems are considered as carbon sinks that may mitigate the impacts of increased atmospheric CO2 concentration ([CO2]). However, it is not clear what their carbon sink capacity will be under extreme climatic conditions. In this study, we used long-term (1998-2013) data from a C3 grassland Free Air CO2 Enrichment (FACE) experiment in Germany to study the combined effects of elevated [CO2] and extreme climatic events (ECEs) on aboveground biomass production. CO2 fertilization effect (CFE), which represents the promoted plant photosynthesis and water use efficiency under higher [CO2], was quantiffied by calculating the relative differences in biomass between the plots with [CO2] enrichment and the plots with ambient [CO2]. Down-regulated CFEs were found when ECEs occurred during the growing season, and the CFE decreases were statistically significant with p well below 0.05 (t-test). Of all the observed ECEs, the strongest CFE decreases were associated with intensive and prolonged heat waves. These findings suggest that more frequent ECEs in the future are likely to restrict the mitigatory effects of C3 grassland ecosystems, leading to an accelerated warming trend. To reduce the uncertainties of future projections, the atmosphere-vegetation interactions, especially the ECEs effects, are emphasized and need to be better accounted.

Whole-Plant Water Use in Field Grown Grapevine: Seasonal and Environmental Effects on Water and Carbon Balance

Water scarcity is a main challenge in vineyards sustainability in most of the grapevine areas now and even more in near future due to climatic change perspectives. In consequence, water use efficiency (WUE) measurements are of the highest interest to improve the sustainability of this crop. The vast majority of WUE measurements relays on measurements of leaf carbon and water fluxes at leaf-level. However, less data are available at the whole-plant level, and for the moment those data are not totally coincident with conclusions reached at leaf scale. In this study, we used whole-plant chambers able to enclose an entire plant of 12 years old to measure at the same time water and carbon fluxes under realistic field grown conditions. The main objectives were to identify the technical issues interfering the whole-plant measurements and track the environmental and other abiotic factors that can affect water and carbon balance, i.e., WUE at the whole-plant scale. To achieve those objectives, we measured whole-plant water and carbon fluxes in grapevine exposed to two different water regimes at three phenological stages [pea size (July), ripening (August), and harvest (September)]. In September, measurements were repeated under high CO2 to also check its effect at the whole-plant scale. The results indicate that water and carbon fluxes are well coordinated under both water availability treatments. Under drought conditions, both fluxes were drastically reduced, but surprisingly the estimated WUE resulted not improved but decreased, contrarily to what is shown at the leaf scale. The phenology (September) also strongly decreased both water and carbon fluxes when compared to measurements in July. We hypostatized that harvest load respiration rates could have an important weight on the whole-plant net carbon exchange (NCE). Finally, high CO2 measurements, after correction for leaks, indicated an increase of whole-plant NCE as well as increased whole-plant WUE, as expected. Several technical issues were identified, like 1/instability of [CO2] during the night period that prevent robust estimation of whole-plant respiration and 2/condensation during last night and sun-rise hours which may affect the estimation of daily plant transpiration.

Elevated atmospheric CO2 promoted speciation in mosquitoes (Diptera, Culicidae)

Mosquitoes are of great medical significance as vectors of deadly diseases. Despite this, little is known about their evolutionary history or how their present day diversity has been shaped. Within a phylogenetic framework, here we show a strong correlation between climate change and mosquito speciation rates: the first time to our knowledge such an effect has been demonstrated for insects. Information theory reveals that although climate change is correlated with mosquito evolution there are other important factors at play. We identify one such driver to be the rise of mammals, which are predominant hosts of Culicidae. Regardless of the precise mechanism, we demonstrate a strong historical association. This finding, taken in combination with projected rises in atmospheric CO₂ from anthropogenic activity, has important implications for culicid vector distributions and abundance, and consequently for human health.

Chufei Tang and Katie E. Davis et al. show that an elevated atmospheric CO₂ promotes the speciation rates of mosquitoes. They demonstrate that climate change can expedite the evolution of mammalian disease vectors, potentially increasing vector−pathogen interactions and affecting human health.

Crop quality under rising atmospheric CO2

Crops grown under elevated CO₂ (eCO₂) typically exhibit enhanced yields but at the same time decreased nutritional quality. The latter effect has often been explained as a growth dilution phenomenon, but this cannot be the only process involved since crop nutrient concentrations are decreased also when production is unaffected by eCO₂. We review the current knowledge on eCO₂ effects on crop nutritional quality with focus on the current understanding of the possible mechanisms and processes causing these effects. Emphasis is on crop nitrogen (N) and protein concentrations but effects on other nutrients and how they compare with those on N are also covered.

Photosynthesis and carbon allocation are both important predictors of genotype productivity responses to elevated CO2 in Eucalyptus camaldulensis

Intraspecific variation in biomass production responses to elevated atmospheric carbon dioxide (eCO2) could influence tree species' ecological and evolutionary responses to climate change. However, the physiological mechanisms underlying genotypic variation in responsiveness to eCO2 remain poorly understood. In this study, we grew 17 Eucalyptus camaldulensis Dehnh. subsp. camaldulensis genotypes (representing provenances from four different climates) under ambient atmospheric CO2 and eCO2. We tested whether genotype leaf-scale photosynthetic and whole-tree carbon (C) allocation responses to eCO2 were predictive of genotype biomass production responses to eCO2. Averaged across genotypes, growth at eCO2 increased in situ leaf net photosynthesis (Anet) (29%) and leaf starch concentrations (37%). Growth at eCO2 reduced the maximum carboxylation capacity of Rubisco (-4%) and leaf nitrogen per unit area (Narea, -6%), but Narea calculated on a total non-structural carbohydrate-free basis was similar between treatments. Growth at eCO2 also increased biomass production and altered C allocation by reducing leaf area ratio (-11%) and stem mass fraction (SMF, -9%), and increasing leaf mass area (18%) and leaf mass fraction (5%). Overall, we found few significant CO2 × provenance or CO2 × genotype (within provenance) interactions. However, genotypes that showed the largest increases in total dry mass at eCO2 had larger increases in root mass fraction (with larger decreases in SMF) and photosynthetic nitrogen-use efficiency (PNUE) with CO2 enrichment. These results indicate that genetic differences in PNUE and carbon sink utilization (in roots) are both important predictors of tree productivity responsiveness to eCO2.

Similar photosynthetic response to elevated carbon dioxide concentration in species with different phloem loading strategies

Species have different strategies for loading sugars into the phloem, which vary in the route that sugars take to enter the phloem and the energetics of sugar accumulation. Species with passive phloem loading are hypothesized to have less flexibility in response to changes in some environmental conditions because sucrose export from mesophyll cells is dependent on fixed anatomical plasmodesmatal connections. Passive phloem loaders also have high mesophyll sugar content, and may be less likely to exhibit sugar-mediated down-regulation of photosynthetic capacity at elevated CO₂ concentrations. To date, the effect of phloem loading strategy on the response of plant carbon metabolism to rising atmospheric CO₂ concentrations is unclear, despite the widespread impacts of rising CO₂ on plants. Over three field seasons, five species with apoplastic loading, passive loading, or polymer-trapping were grown at ambient and elevated CO₂ concentration in free air concentration enrichment plots. Light-saturated rate of photosynthesis, photosynthetic capacity, leaf carbohydrate content, and anatomy were measured and compared among the species. All five species showed significant stimulation in midday photosynthetic CO₂ uptake by elevated CO₂ even though the two passive loading species showed significant down-regulation of maximum Rubisco carboxylation capacity at elevated CO₂. There was a trend toward greater starch accumulation at elevated CO₂ in all species, and was most pronounced in passive loaders. From this study, we cannot conclude that phloem loading strategy is a key determinant of plant response to elevated CO₂, but compelling differences in response counter to our hypothesis were observed. A phylogenetically controlled experiment with more species may be needed to fully test the hypothesis.

Expression level of Rubisco activase negatively correlates with Rubisco content in transgenic rice

The relationship between ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase (Rca) levels was studied using transgenic rice overexpressing maize Rca (OX-mRca) and knockdown transgenic rice expressing antisense Rca (KD-Rca). The ratio of Rubisco to total soluble protein was lower in OX-mRca, whereas it was higher in KD-Rca than in WT, indicating that Rca expression was negatively correlated with Rubisco content. The expressions of other Calvin-Benson-Bassham cycle enzymes such as sedoheptulose-1,7-bisphosphatase and phosphoribulokinase analyzed by immunoblotting did not show such a negative correlation with Rca, suggesting that the effect of Rca on protein expression may be specific for Rubisco. Although Rubisco content was decreased in OX-mRca, the transcript levels of the Rubisco large subunit (OsRbcL) and the Rubisco small subunit mostly increased in OX-mRca as well as in KD-Rca. Additionally, polysome loading of OsRbcL was slightly higher in OX-mRca than it was in WT, suggesting that the OsRbcL translation activity was likely stimulated by overexpression of Rca. ³⁵S-methionine labeling experiments demonstrated that there was no significant difference in the stability of newly synthesized Rubisco among genotypes. However, ³⁵S-methionine-labeled Rubisco was marginally decreased in OX-mRca and increased in KD-Rca compared to the WT. These results suggest that Rca negatively affects the Rubisco content, possibly in the synthesis step.

Elevated and super-elevated CO2 differ in their interactive effects with nitrogen availability on fruit yield and quality of cucumber

BACKGROUND

Elevated carbon dioxide (CO₂ ) and nitrogen (N) availability can interactively promote cucumber yield, but how the yield increase is realized remains unclear, whilst the interactive effects on fruit quality are unknown. In this study, cucumber plants (Cucumis sativus L. cv. Jinmei No. 3) were grown in a paddy soil under three CO₂ concentrations - 400 (ambient CO₂ ), 800 (elevated CO₂ , eCO₂ ) and 1200 µmol mol^-1 (super-elevated CO₂ ) - and two N applications - 0.06 (low N) and 0.24 g N kg^-1 soil (high N).

RESULTS

Compared with ambient CO₂ , eCO₂ increased yield by 106% in high N but the increase in total biomass was only 33%. This can result from greater carbon translocation to fruits from other organs, indicated by the increased biomass allocation from stems and leaves, particularly source leaves, to fruits and the decreased concentrations of fructose and glucose in source leaves. Super-elevated CO₂ reduced the carbon allocation to fruits thus yield increase (71%). Additionally, eCO₂ also increased the concentrations of fructose and glucose in fruits, maintained the concentrations of dietary fiber, phosphorus, potassium, calcium, magnesium, sulfur, manganese, copper, molybdenum and sodium, whilst it decreased the concentrations of nitrate, protein, iron, and zinc in high N. Compared with eCO₂ , super-elevated CO₂ can still improve the fruit quality to some extent in low N availability.

CONCLUSIONS

Elevated CO₂ promotes cucumber yield largely by carbon allocation from source leaves to fruits in high N availability. Besides a dilution effect, carbon allocation to fruits, carbohydrate transformation, and nutrient uptake and assimilation can affect the fruit quality. © 2018 Society of Chemical Industry.

Elevated carbon dioxide and warming impact silicon and phenolic-based defences differently in native and exotic grasses

Global climate change may increase invasions of exotic plant species by directly promoting the success of invasive/exotic species or by reducing the competitive abilities of native species. Changes in plant chemistry, leading to altered susceptibility to stress, could mediate these effects. Grasses are hyper-accumulators of silicon, which play a crucial function in the alleviation of diverse biotic and abiotic stresses. It is unknown how predicted increases in atmospheric carbon dioxide (CO₂ ) and air temperature affect silicon accumulation in grasses, especially in relation to primary and secondary metabolites. We tested how elevated CO₂ (eCO₂ ) (+240 ppm) and temperature (eT) (+4°C) affected chemical composition (silicon, phenolics, carbon and nitrogen) and plant growth in eight grass species, either native or exotic to Australia. eCO₂ increased phenolic concentrations by 11%, but caused silicon accumulation to decline by 12%. Moreover, declines in silicon occurred mainly in native species (-19%), but remained largely unchanged in exotic species. Conversely, eT increased silicon accumulation in native species (+19%) but decreased silicon accumulation in exotic species (-10%). Silicon and phenolic concentrations were negatively correlated with each other, potentially reflecting a defensive trade-off. Moreover, both defences were negatively correlated with plant mass, compatible with a growth-defence trade-off. Grasses responded in a species-specific manner, suggesting that the relative susceptibility of different species may differ under future climates compared to current species rankings of resource quality. For example, the native Microlaena stipoides was less well defended under eCO₂ in terms of both phenolics and silicon, and thus could suffer greater vulnerability to herbivores. To our knowledge, this is the first demonstration of the impacts of eCO₂ and eT on silicon accumulation in grasses. We speculate that the greater plasticity in silicon uptake shown by Australian native grasses may be partly a consequence of evolving in a low nutrient and seasonally arid environment.

Disentangling the effects of acidic air pollution, atmospheric CO2 , and climate change on recent growth of red spruce trees in the Central Appalachian Mountains

In the 45 years after legislation of the Clean Air Act, there has been tremendous progress in reducing acidic air pollutants in the eastern United States, yet limited evidence exists that cleaner air has improved forest health. Here, we investigate the influence of recent environmental changes on the growth and physiology of red spruce (Picea rubens Sarg.) trees, a key indicator species of forest health, spanning three locations along a 100 km transect in the Central Appalachian Mountains. We incorporated a multiproxy approach using 75-year tree ring chronologies of basal tree growth, carbon isotope discrimination (∆¹³ C, a proxy for leaf gas exchange), and δ¹⁵ N (a proxy for ecosystem N status) to examine tree and ecosystem level responses to environmental change. Results reveal the two most important factors driving increased tree growth since ca. 1989 are reductions in acidic sulfur pollution and increases in atmospheric CO₂ , while reductions in pollutant emissions of NO_x and warmer springs played smaller, but significant roles. Tree ring ∆¹³ C signatures increased significantly since 1989, concurrently with significant declines in tree ring δ¹⁵ N signatures. These isotope chronologies provide strong evidence that simultaneous changes in C and N cycling, including greater photosynthesis and stomatal conductance of trees and increases in ecosystem N retention, were related to recent increases in red spruce tree growth and are consequential to ecosystem recovery from acidic pollution. Intrinsic water use efficiency (iWUE) of the red spruce trees increased by ~51% across the 75-year chronology, and was driven by changes in atmospheric CO₂ and acid pollution, but iWUE was not linked to recent increases in tree growth. This study documents the complex environmental interactions that have contributed to the recovery of red spruce forest ecosystems from pervasive acidic air pollution beginning in 1989, about 15 years after acidic pollutants started to decline in the United States.

Effects of Elevated CO2 on Nutritional Quality of Vegetables: A Review

Elevated atmospheric CO2 (eCO2) enhances the yield of vegetables and could also affect their nutritional quality. We conducted a meta-analysis using 57 articles consisting of 1,015 observations and found that eCO2 increased the concentrations of fructose, glucose, total soluble sugar, total antioxidant capacity, total phenols, total flavonoids, ascorbic acid, and calcium in the edible part of vegetables by 14.2%, 13.2%, 17.5%, 59.0%, 8.9%, 45.5%, 9.5%, and 8.2%, respectively, but decreased the concentrations of protein, nitrate, magnesium, iron, and zinc by 9.5%, 18.0%, 9.2%, 16.0%, and 9.4%. The concentrations of titratable acidity, total chlorophyll, carotenoids, lycopene, anthocyanins, phosphorus, potassium, sulfur, copper, and manganese were not affected by eCO2. Furthermore, we propose several approaches to improving vegetable quality based on the interaction of eCO2 with various factors, including species, cultivars, CO2 levels, growth stages, light, O3 stress, nutrient, and salinity. Finally, we present a summary of the eCO2 impact on the quality of three widely cultivated crops, namely, lettuce, tomato, and potato.

Subtropical Tritrophic Interactions Under Elevated CO2 and Temperature Conditions

The effects of climate change and extreme weather conditions on plants and animals have been documented extensively. However, the possible effects of these factors on plant-insect interactions in subtropical regions are relatively unexplored. The present study investigated the consequences of elevated CO2 and temperature on a tritrophic system (plant-insect-parasitoid) in subtropical regions. The experimental conditions were as follows: ambient CO2, 500 ppm; elevated CO2, 1,000 ppm; ambient temperature, 24/21°C (day/night); and elevated temperature, 29/26°C (day/night). Brassica oleracea var. italica foliar primary metabolites were quantified 6 wk after germination and insect feeding bioassays were subsequently conducted. Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae were fed directly on these plants until pupal development. In addition, the second instar S. litura larvae were exposed to the parasitoid Snellenius manilae (Ashmead) (Hymenoptera: Braconidae) under the same plant treatment conditions. The results suggested that elevated CO2 has a major influence on plant performance and foliar quality. Elevated CO2 also affected the leaf area, foliar fresh and dry weights, and total nitrogen and carbohydrate contents. Elevated temperature reduced the larval development time and increased the growth rate of S. litura. Sn. manilae had a higher parasitism rate and shorter development time at elevated temperature compared with ambient temperature. These results suggested that the dynamic and communal structure of S. litura and its parasitoids requires comprehensive evaluation in terms of the changes in nutritional quality (bottom-up control) caused by the interactive effects of CO2 and temperature.